Sommaire:

Rotation and convection have important consequences for stellar internal structure and evolution. On the first side, rotation, through the centrifugal acceleration, deforms the star and counteracts the gravitational force, mimicking a lower mass star. Most importantly, meridional circulations and rotation-induced turbulence mix chemical elements, extending the life of the star and affecting stellar age determinations, one of the most important problems in astrophysics. Lastly, the interaction between rotation and convection generates magnetic fields, maintaining a dynamo and influencing on the survival of stellar atmospheres. Important effort have been devoted to improving the rotation modelling in the stellar evolution code Cesam2k20 (formerly known as CESTAM).It now accounts for the effect of 2D geometry of a star distorted by rotation, making it a framework to test all the processes envisaged to transport angular momentum.
On the 2nd side, convection is poorly modelled in stellar evolution code. From a highly turbulent process, it is often reduced to a laminar flow, whose energy flux is controlled by a unique free parameter, fixed along evolution. The value of this paramter is not physically constrains, but has a strong impact on estimation of stellar global properties. A new method, the entropy callibration, was developped to constrain the value of the convection parameter with prescription of entropy in the deep convective zone, obtained from 3D simulations of stellar atmospheres. With the entropy calibration, now available in Cesam2k20, the convection parameter vary along evolution, and is linked to physical quantities, removing an important source of uncertainties.

Pour plus d'informations, merci de contacter Deal M.